The present invention relates to a method for manufacturing a group III-V compound semiconductor and a semiconductor device using the same.
In recent years, there is an increasing demand for a semiconductor laser element that outputs blue-violet light as a light source for a high-density optical disk of the next generation. Particularly, active researches and developments have been made for a light-emitting element made of a gallium nitride (GaN)-based group III-V compound semiconductor capable of operating in a relatively short wavelength range, i.e., a wavelength range of blue-violet light.
Since a gallium nitride-based semiconductor is chemically stable and has a high hardness, a wet etching method, which is used in a manufacturing process for other group III-V compound semiconductors such as gallium arsenide (GaAs) or indium phosphide (InP), cannot be used. Therefore, a dry etching method is usually used for etching a gallium nitride-based semiconductor.
However, a dry etching method, as compared with a wet etching method, is difficult to control so as to selectively etch a semiconductor layer to be etched or to stop etching at a desired thickness, for example.
For example, influences of the etching stop position in a semiconductor layer to be etched on the operating characteristics of a gallium nitride-based semiconductor laser element are reported in an article xe2x80x9cProc. of the 61st Meeting of the Japan Society of Applied Physics, Vol. 1, p.325 (7p-L-4), September 2000xe2x80x9d. In this article, it is stated that it is necessary to accurately control the post-etching thickness of a p-type cladding layer provided on an active layer in order to reduce the operating current of a semiconductor laser element.
Another article xe2x80x9cProc. of the 47th Meeting of the Japan Society of Applied Physics and Related Societies, Vol. 1, p.378 (30a-YQ-7), March 2000xe2x80x9d contains a report on a measurement of a real-time depth in dry etching for a nitride-based semiconductor laser element. However, the article fails to report on a method for controlling the etching on a semiconductor layer.
A conventional dry etching process for a nitride-based semiconductor is performed on a layered structure of a plurality of semiconductor layers having different mixed crystal compositions such as AlxGa1xe2x88x92xN (where 0.x.1). Therefore, the etching rates for the respective semiconductor layers are measured in advance, and the process is performed while managing the etching time based on the measured etching rates.
However, with the conventional dry etching method for a group III-V compound semiconductor, it is necessary to measure and manage the etching rate for each of the semiconductor layers having different compositions. In addition, it is necessary to control and manage dry etching conditions such as the temperature and the plasma state, thereby decreasing the productivity and the yield and increasing the cost.
An object of the present invention is to solve the problems in the prior art and to make it possible to easily and reliably control an etching process on a group III-V compound semiconductor.
In order to achieve the object, the present invention provides an etching stop layer in at least a portion of an area under a group III-V compound semiconductor to be etched.
Specifically, a method for manufacturing a semiconductor of the present invention includes: a first step of forming an etching stop layer on a first semiconductor layer; and a second step of forming a second semiconductor layer made of a group III-V compound semiconductor on the etching stop layer, wherein an etching rate for the etching stop layer by dry etching is less than an etching rate for the second semiconductor layer.
According to the method for manufacturing a semiconductor of the present invention, the etching rate for the etching stop layer by dry etching is less than the etching rate for the second semiconductor layer. Therefore, it is possible to selectively dry-etch the second semiconductor layer, whereby it is possible to prevent the first semiconductor layer from being overetched. Thus, the controllability of the dry etching process on the second semiconductor layer, which is made of a group III-V compound semiconductor, is improved.
In the method for manufacturing a semiconductor of the present invention, it is preferred that in the first step, the etching stop layer is formed by using a group III-V compound semiconductor containing aluminum. When the etching stop layer is made of a group III-V compound semiconductor, the etching stop layer becomes a compound semiconductor equivalent to the second semiconductor layer, thereby eliminating the possibility for the crystallinity of the second semiconductor layer to be deteriorated. Moreover, the etching resistance of the group III-V compound semiconductor containing aluminum is improved, thereby resulting in a good selectivity of dry etching on the second semiconductor layer. In addition, it is possible to form the etching stop layer using a normal semiconductor manufacturing apparatus as it is.
In such a case, it is preferred that: the second semiconductor layer contains aluminum; and in the first step, the etching stop layer is formed so that an aluminum composition of the etching stop layer is greater than an aluminum composition of the second semiconductor layer. In this way, since a group III-V compound semiconductor that has the greater aluminum composition has a smaller etching rate, the etching stop layer can reliably exert its function.
In the method for manufacturing a semiconductor of the present invention, it is preferred that in the first step, the etching stop layer is a super lattice layer obtained by alternately layering AlxGa1xe2x88x92xN (where 0.x.1) and AlyGa1xe2x88x92yN (where 0.y.1 and xxe2x89xa0y) on one another.
In such a case, it is preferred that the etching stop layer is a reflector mirror having a thickness such as to reflect light whose wavelength is equal to or greater than about 360 nm and less than or equal to 500 nm. In this way, when a laser element is produced from the manufactured semiconductor, the spontaneous emission light emitted from the laser element can be effectively guided as induced emission light while preventing it from leaking to the outside.
In the method for manufacturing a semiconductor of the present invention, it is preferred that the etching stop layer is made of an element included in a group III-V nitride semiconductor and an impurity element that determines a conductivity of the group III-V nitride semiconductor. In this way, where the second semiconductor layer is a group III-V nitride semiconductor, it is not necessary to provide an additional material for forming the etching stop layer. Therefore, it is possible to easily and reliably form the etching stop layer without having to add any modifications to the semiconductor manufacturing apparatus.
In such a case, it is preferred that the element included in the group III-V nitride semiconductor is nitrogen, and the impurity element is silicon. In this way, where the second semiconductor layer is made of a group III-V nitride semiconductor, the etching stop layer can be provided by an insulative film made of silicon nitride, for example, by using ammonium as a nitrogen source and a silane gas as a silicon source, for example. As a result, the etching selectivity ratio with respect to the second semiconductor layer can be increased, thereby improving the etching controllability for the second semiconductor layer.
Alternatively, in such a case, it is preferred that the impurity element is magnesium. In this way, the etching stop layer exhibits a p-conductivity type, and it is possible to obtain an etching stop layer having a good conductivity, whereby when a semiconductor element is formed from the obtained semiconductor, it is less likely to adversely affect the operating characteristics of the element.
In such a case, it is preferred that an impurity concentration of magnesium is about 1xc3x971020 cmxe2x88x923 or more. When the magnesium impurity concentration in the group III-V nitride semiconductor is set to be about 1xc3x971020 cmxe2x88x923 or more, the etching rate decreases, thereby improving the etching controllability for the second semiconductor layer.
In the method for manufacturing a semiconductor of the present invention, it is preferred that: the method further includes a third step of performing a dry etching process on the second semiconductor layer, before the second step; and in the third step, the etching process on the second semiconductor layer is stopped upon detecting the etching stop layer. In this way, the etching stop layer can be determined during the dry etching process on the second semiconductor layer, whereby it is possible to reliably etch the second semiconductor layer.
In such a case, it is preferred that the third step includes the steps of: irradiating a surface of the second semiconductor layer with a laser beam; receiving photoluminescence light emitted through excitation by the laser beam; and assuming that a surface of the etching stop layer has been exposed by detecting a change in a wavelength of the received photoluminescence light.
Alternatively, in such a case, it is preferred that the third step includes the steps of: irradiating a surface of the second semiconductor layer with X rays; measuring a diffraction angle of the X rays; and assuming that a surface of the etching stop layer has been exposed by detecting a change in the diffraction angle of the X rays.
A method for manufacturing a semiconductor device of the present invention includes the steps of: sequentially forming a first semiconductor layer including an active layer, an etching stop layer, and a second semiconductor layer made of a group III-V compound semiconductor; and selectively dry-etching the second semiconductor layer, wherein an etching rate for the etching stop layer by dry etching is less than an etching rate for the second semiconductor layer.
According to the method for manufacturing a semiconductor device of the present invention, the second semiconductor layer, which is made of a group III-V compound semiconductor, is formed on the etching stop layer. The etching rate for the etching stop layer by dry etching is less than the etching rate for the second semiconductor layer. Therefore, it is possible to selectively dry-etch the second semiconductor layer, whereby the second semiconductor layer will not be left in the etching area while the first semiconductor layer will not be etched. Thus, the controllability of the dry etching process on the second semiconductor layer, which is made of a group III-V compound semiconductor, is improved.